Epihalohydrin polymers are well known commercial elastomers which have solvent, fuel, oil, ozone and heat resistance coupled with low temperature flexibility and easy formability. These elastomers offer a combination of many of the desirable properties of nitrile, polychloroprene, polysulfide, and polyacrylic rubbers.
The epihalohydrin homopolymers are generally resistant to ozone, have extremely low gas permeability, and are well suited for gaskets, oil-field specialties, diaphragms, and pump and valve parts. The epihalohydrin copolymers generally have superior low temperature flexibility for automotive and refrigeration applications such as fuel pump diaphragms, gasoline hose, and oil seals. Paper and printing rolls are other uses. Blends of the homopolymers and copolymers are useful for high temperature conveyor belts and automotive mounts and vibration isolators.
For certain applications, however, it is desirable that polymers of epihalohydrin exhibit lower viscosity on curing and higher hardness after curing. The lower viscosity on curing facilitates flow of the material in a mold and thus allows for more efficient molding. Higher hardness is desirable to achieve product characteristics. It was discovered that these objectives can be met by blending polymers of epihalohydrin with polymers of lower alkylenes and curing such blends with organic peroxides.
The concept of blending polymers of epihalohydrin with polymers of lower alkylenes followed by peroxide cure is unconventional since epihalohydrin polymers are polar whereas alkylene polymers are nonpolar and the two classes of polymers are considered to be incompatible. On mixing an epihalohydrin polymer with an alkylene polymer, it would be expected that no physical intermixing would take place and that there would be phase separation.
The Oetzel U.S. Pat. No. 4,251,648 discloses that blends of unsaturated epihalohydrin polymers with other elastomers can be co-cured with a peroxide. The epihalohydrin polymers contemplated by Oetzel for blending with other peroxide-curable elastomers are prepared in the presence of an unsaturated glycidyl ether which renders the polymers unsaturated. These polymers can also be prepared in presence of an alkylene oxide, such as ethylene oxide. The other elastomers include various materials disclosed at top of col. 6 of the Oetzel patent such as natural rubber, polyisoprene, the butadiene polymers, polychloroprene, olefin polymers such as polyethylene, chlorinated polyethylene, ethylene and propylene copolymers, etc. The invention disclosed herein relates to peroxide-curable blends of saturated epihalohydrin polymers with lower polyolefins. Contrary to the disclosure in the Oetzel patent, it was discovered that ethylene/propylene rubber does not provide the desired improvement in viscosity and hardness and for this reason, it is excluded from the scope of the invention claimed herein.
U.S. Pat. No. 4,032,479 to Bunnomori et al, discloses blends of epihalohydrin homopolymers and copolymers with other rubbers such as natural rubbers, synthetic rubbers, and peroxide curable saturated rubbers. Examples of peroxide-curable saturated rubbers are chlorinated polyethylene, chlorosulfonated polyethylene, acrylic rubbers comprising an acrylate ester as a main component, and an ethylene/propylene rubber. The curing system for the epihalohydrin polymers and blends thereof with other rubbers includes a salt of an ethylenically unsaturated monocarboxylic acid with 1,8-diazabicyclo (5,4,0) undecene-7 with an organic peroxide. The reason for the complex curing system resides in the fact that Bunnomori et al could not put an organic peroxide to practical use as a curing agent for homopolymers or copolymers of epihalohydrins.
Recently filed patent application of J. P. Barnhouse, the inventor herein, entitled "Epihalohydrin Polymers", which was filed Sept. 15, 1982 and bears Ser. No. 418,312, discloses and claims a composition that is devoid of an unsaturation component, such as an unsaturated glycidyl ether, said composition comprising a polymer of an epihalohydrin, an acid acceptor, an unsaturated polyfunctional coagent, and a peroxide curing agent.